The main thing is to drain out all the horrible ancient oil - which has been broken down by years of hard labour squeezing through small orifices. I use 20W50 in the dampers and this gives far better damping and I have never had any problems - but do check the damper mounting bolts are nice and tight anyway. Others will tell you to only use the 'correct' oil.

Be careful not to lose the little springs and packing washers that come out with the valves which you will remove to drain the units - place a dish under to catch everything. then bounce the car to work out the old fluid - and flush some new stuff through too before refitting the valves and filling up. Lots more bouncing then to work all the air out - and check again in a week's time for final topping up.